Seek-scan probe (SSP) memory is a type of memory that uses a non-volatile storage media as the data storage mechanism and offers significant advantages in both cost and performance over conventional charge storage memories. Typical SSP memories include storage media made of materials that can be electrically switched between two or more states having different electrical characteristics, such as resistance or polarization dipole direction.
SSP memories are written to by passing an electric current through the storage media or applying an electric field to the storage media. Passing a current through the storage media is typically accomplished by passing a current between a sharp probe tip on one side of the storage media and an electrode on the other side of the storage media. Current SSP memories use probe tips positioned on the free end of one or more MEMS probes. In an idle state each MEMS probe maintains the probe tip at a certain distance from the storage media, but before the electric field or current can be applied to the storage media the probe tip must usually be brought close to, or in some cases in direct contact with, the storage media. To maximize the number of data bits that can be written to the storage media (i.e., the storage density), it is advantageous for the probe tip to be as sharp as possible so that the data bits written in the storage media will be as small as possible.
In some SSP memories, to obtain a sufficient signal-to-noise ratio for read/write/erase operations on the storage media, it is advantageous to have electrical circuitry such as amplifiers, signal processors, etc, close to, adjacent to, or under the MEMS probe. One way of achieving this proximity is to place the MEMS probes on a conductive metal oxide semiconductor (CMOS) wafer in or on which the needed circuitry has already been formed. Unfortunately, placing sharp-tipped MEMS probes on a CMOS wafer has been exceedingly difficult because the high-temperature process required to make sharp-tipped probes are incompatible with the post-processing requirements of CMOS wafers; in essence, the high-temperature processes alter or destroy circuitry or other elements formed on the CMOS wafer.
One solution to putting sharp-tipped MEMS probes on a CMOS wafer has been to fabricate the MEMS probes separately and then transfer them and mount them on the surface of a CMOS wafer. This, however, is a difficult and time-consuming task that results in high costs and low yields.